Botanic Garden unveils perennial project

The 10-month project that uses native plants to knit the soil surrounding the garden's North Lake into a firm, erosion-resistant mixture that also enhances the habitat for animal life.

The Chicago Botanic Garden recently unveiled the largest perennial planting in its 40-year history — a 10-month project that uses native plants to knit the soil surrounding the garden's North Lake into a firm, erosion-resistant mixture that also enhances the habitat for animal life.

The experts who engineered the project at the Glencoe site say it can be a guide for similar efforts at thousands of lakes and ponds in northern Illinois that suffer from erosion.

The goal is to make a friendly environment for freshwater inhabitants like turtles, fish and reptiles, as well as migratory birds, like a great egret that has begun calling North Lake its home.

After draining 54 million gallons of water from the lake in December, the Botanic Garden and the Army Corps of Engineers collaborated to regrade 1.25 miles of the lake's edge to create shelves for underwater plantings to accompany shoreline plants — more than 120,000 perennials in total, officials said.

Erosion traditionally is controlled with boulders and sheet piling that extends above the water's surface. But with this project, the Botanic Garden opted for "bioengineering" techniques that also would enhance water quality and provide a healthy habitat for plants and animals.

Bob Kirschner, director of restoration ecology at the Botanic Garden, hopes the project can act like a testing laboratory for others to learn from.

"We want to make all the mistakes that can be made for the end users so they can look at what we did here and go home knowing it can work," he said.

Erosion is largely due to fluctuating water levels, and it's common among thousands of small lakes and retention ponds across the area, Kirschner said. At the Botanic Garden, a heavy rain can cause the water level to rise up to 5 feet, he said. Without proper grading or plants along the shore, changing water levels can cause the bank to collapse.

"You end up almost with a vertical bank, and that will essentially perpetuate itself forever because there are no plants to hold the soil in place and now the steepness of the grade is so extreme that plants can't move in," Kirschner said.

He said choosing the correct plant life is essential in establishing a long-lasting shoreline that withstands the water and the work of animals such as muskrats, deer, geese and ducks.

Project designers selected plants from more than 200 native species, some of which extend their roots nearly six feet down and "knit the soil in the shoreline together" to protect it from erosion, Kirschner said. Custom plastic meshing protects the shallow depths from bottom-feeding fish like common carp.

More than 1,000 shrubs also were installed because of their value to migratory birds that follow the Lake Michigan coast, he added.

As the Botanic Garden celebrated the completion of the project on a recent afternoon, the sixth in a series of shoreline restorations that began in 1999, a great blue heron flew across the lake, providing an unexpected example of what a thriving wetland can provide — even one within earshot of a major highway.

John Rogner, assistant director of the Illinois Department of Natural Resources, noted the difficulty in successfully establishing plantings in an urban wetland, and that Kirschner and his team's work on the project will benefit others.

"I think you all have written a book on how to do these things," Rogner said. "You're the tip of the spear and we all as wetland restoration practitioners have a lot to learn from your experiences here."

Kirschner said he hopes the Botanic Garden can help influence private owners, as well as public entities like park districts, to use similar techniques on their shorelines.

"This is entirely applicable for implementation on a small scale in a homeowner's pond," Kirschner said. "It's not going to cost them $59, but for a lot less money than oftentimes the structural enclosures or stone and sheet piling, it can be just as effective a solution — and we think looks nicer as well."